Zimbabwe's new president, Emmerson Mnangagwa, called for public unity to revive the country's sickly economy as his new cabinet took office on Monday.

"I have sworn in a new cabinet just to finish the term of the former president, which is a period of six to seven months," Mnangagwa said after the new ministers took the oath of office at state house.

"I believe with my team we will stand up to the challenge."

"I want them (Zimbabweans) to be united, we must grow our economy," he added.

Mnangagwa was seen as favourite to succeed long-time ruler Robert Mugabe but then fell out with his boss.

Mugabe dismissed him after the then first lady, Grace Mugabe, accused him of plotting to topple her husband.

He briefly went into exile, returning after the army stepped in and the ruling party expelled Mugabe and a coterie of allies. The veteran ruler resigned on November 21 after 37 years in power.

Mnangagwa, chosen by the ruling party to replace Mugabe, appointed a new cabinet on Thursday.

He drew criticism for retaining the majority of ministers who served under 93-year-old Mugabe and appointing officers from the military which played a key role in the events leading to his ascent to power.

The 22-member cabinet includes Air Marshal Perrance Shiri, who was appointed agriculture and lands minister, and Major General Sibusiso Moyo, who is now in charge of foreign affairs.

Both officials had to relinquish their army positions, as they are not permitted to hold two posts.

"When I was in the military I was under (the) ministry of defence, which is part of government and who says military should never be politicians," Shiri told reporters after he was sworn-in.

"I am Zimbabwean, I have got every right to participate in the country's politics," he said.

The new president also reinstated prosecutor general, Ray Goba, who was named under Mugabe in September but whose appointment was rescinded the following month.

Mnangagwa has issued a three-month ultimatum for the return of funds siphoned out of the country by individuals and corporates.